Transmission, hybrid drivetrain and drivetrain for an electric vehicle

ABSTRACT

A transmission includes a main gear set, an auxiliary gear set and an electric motor with a rotor and a stator. A third shaft of the main gear set is connected to a transmission output shaft, and a first shaft of the auxiliary gear set is connected to the rotor. When a second shaft of the auxiliary gear set is connected to a first shaft of the main gear set, a third shaft of the auxiliary gear set is constantly connected to the third shaft of the main gear set or a fourth shaft of the main gear set. When the second shaft of the auxiliary gear set is connected to the third shaft of the main gear set, the third shaft of the auxiliary gear set is constantly connected to the fourth shaft of the main gear set.

FIELD OF THE INVENTION

The invention relates generally to a transmission with a transmissioninput shaft and a transmission output shaft, a main gear set, anauxiliary gear set, and an electric motor with a rotor and a stator,whereas the transmission comprises a first power path and a second powerpath between the transmission input shaft and the main gear set, whereasthe main gear set features a first and a second planetary gear set witha total of four shafts designated in the order of rotational speeds asthe first, second, third and fourth shafts, whereas the first power pathis connectable through a first shift element to the fourth shaft of themain gear set and through a second shift element to the second shaft ofthe main gear set, whereas the second power path is connectable througha third shift element to the first shaft of the main gear set andthrough a fourth shift element to the second shaft of the main gear set,whereas the third shaft of the main gear set is connected to thetransmission output shaft, whereas the auxiliary gear set features aplanetary gear set with a first, second and third shafts, and whereasthe first shaft of the auxiliary gear set is constantly connected to therotor. The invention also relates generally to a drive train for a motorvehicle with a transmission.

BACKGROUND

Herein, a transmission in particular designates a multi-speedtransmission, with which a predetermined number of gears, thus fixedtransmission ratio relationships between a transmission input shaft andthe transmission output shaft, are automatically shiftable byshiftelements. Under certain circumstances, such a transmission may also havea variable transmission ratio between the transmission input shaft andthe transmission output shaft. Herein, the shift elements comprise, forexample, clutches or brakes. Such transmissions are primarily used inautomotive applications, in order to adjust the rotational speed andtorque output capabilities of the drive unit to the driving resistanceof the motor vehicle in a suitable manner.

From patent application DE 10 2012 201 377 A1 of the applicant, atransmission with a transmission input shaft and a transmission outputshaft, and two power paths between the transmission input shaft and amain gear set with two individual planetary gear sets, with four shaftsdesignated in the order of rotational speeds as the first, second, thirdand fourth shafts is known, whereas the third of the four shafts isconnected to the transmission output shaft. An electric motor isconnected through a planetary transmission at the first shaft of themain gear set.

The task of the invention is to improve the load-shifting behavior ofthe transmission known in the state of the art.

An additional task of the invention is to improve the operating range ofthe transmission, such that, in any gear, the electric motor is able toreceive mechanical power from the transmission output shaft or deliverpower to it.

SUMMARY OF THE INVENTION

A transmission includes at least one transmission input shaft and atransmission output shaft, a main gear set, an auxiliary gear set, andan electric motor with a rotor and a stator.

The main gear set features a first and a second planetary gear set witha total of four shafts designated in the order of rotational speeds asthe first, second, third and fourth shafts. The main gear set is thusformed as a two-carrier/four-shaft transmission. The auxiliary gear setfeatures a planetary gear set with a total of three shafts designated asthe first, second and third shafts. The first shaft of the auxiliarygear set is constantly connected to the rotor.

A “two-carrier/four-shaft transmission” is understood to be a planetarytransmission that is formed from two individual planetary gear setskinematically coupled with each other through exactly two couplingshafts, and with which four of its elements (“shafts”) are freelyaccessible for other transmission elements. Thereby, a coupling shaft isdefined as a constant mechanical connection between one element—thus, asun gear or a carrier or a ring gear—of the first individual planetarygear set with one element—thus, a sun gear or a carrier or a ringgear—of the second individual planetary gear set. The number ofindividual planetary gear sets and the number of free shafts are notdefined by the visual appearance of the transmission, but through itskinematics. In each gear of a two-carrier/four-shaft transmission, twoof the shift elements of the transmission connected to elements of thetwo-carrier/four-shaft transmission must be locked. For the graphicalrepresentation of the kinematics of the transmission, a rotational speeddiagram of the transmission (for example, the Kutzbach diagram knownfrom transmission theory) is typically used. Known embodiments of such atwo-carrier/four-shaft transmission include the so-called “Ravigneauxgear set” and the so-called “Simpson gear set.”

A reduced two-carrier four-shaft transmission is a structural shape of atwo-carrier/four-shaft transmission in which one element—that is, a sungear, a carrier or a ring gear—of the transmission is spared, sinceanother element of the transmission takes over its task, without therebychanging the kinematics. That element that takes over the function ofthe spared element is thus one of the coupling shafts of thetransmission at the same time. A known embodiment of this is theRavigneaux gear set, which features either two sun gears and only onering gear, or two ring gears and only one sun gear.

The transmission features two power paths between the transmission inputshaft and the main gear. Thereby, the two power paths feature adifferent transmission ratio relationship for the transmission inputshaft. The different transmission ratio relationship is achieved by anupstream gear set that is formed as a planetary gear set. The firstpower path is connected through a first shift element to the fourthshaft of the main gear set and through a second shift element to thesecond shaft of the main gear set. The second power path is connectedthrough a third shift element to the first shaft of the main gear setand through a fourth shift element to the second shaft of the main gearset.

In accordance with aspects of the invention, the second shaft of theauxiliary gear set is constantly connected to the first or third shaftof the main gear set. If the second shaft of the auxiliary gear set isconnected to the first shaft of the main gear set, the third shaft ofthe auxiliary gear set is constantly connected to the third or fourthshaft of the main gear set. If the second shaft of the auxiliary gearset is connected to the third shaft of the main gear set, the thirdshaft of the auxiliary gear set is constantly connected to the fourthshaft of the main gear set.

Upon use of a motor vehicle, the transmission input shaft is connectableto a shaft of a drive unit, or is connectable through a clutch, suchthat mechanical power of the drive unit can be supplied to thetransmission input shaft. The drive unit may be formed as an internalcombustion engine and as an electric motor. The transmission outputshaft serves as an interface for transferring mechanical power to thedrive wheels of the motor vehicle.

In the following, a “shaft” is not solely understood as an exemplarycylindrical, rotatably mounted machine element for the transfer oftorques, but is also understood as a general connection element, whichconnects individual components or elements to each other, in particularconnection elements that connect several elements to each other in atorque-proof manner.

A planetary gear set comprises a sun gear, a carrier and a ring gear.Planetary gears, which mesh with the toothing of the sun gear and/orwith the toothing of the ring gear, are rotatably mounted on thecarrier. In the following, a negative gear set describes a planetarygear set with a carrier, on which the planetary gears are rotatablymounted, with a sun gear and a ring gear, whereas the toothing of atleast one of one of the planetary gears meshes both with the toothing ofthe sun gear and with the toothing of the ring gear, by which the ringgear and the sun gear rotate in opposite directions of rotation, if thesun gear rotates with a fixed carrier.

Both sun gear and ring gear of a planetary gear set can also be dividedinto several segments. For example, it is conceivable that the planetarygears mesh with two sun gears, which are not connected to each other. Ofcourse, the rotational speed relationships are identical on bothsegments of the sun gear, as if they were connected to each other.

A positive gear set differs from the negative planetary gear set justdescribed in that the positive gear set features inner and outerplanetary gears, which are rotatably mounted on the carrier. Thereby,the toothing of the inner planetary gears meshes, on the one hand, withthe toothing of the sun gear and, on the other hand, with the toothingof the outer planetary gears. In addition, the toothing of the outerplanetary gears meshes with the toothing of the ring gear. This has theconsequence that, with a fixed carrier, the ring gear and the sun gearrotate in the same direction of rotation.

The stationary transmission ratio defines the rotational speedrelationship between the sun gear and ring gear of a planetary gear witha torque-proof carrier. Since, with a negative gear set, the directionof rotation between the sun gear and ring gear with a torque-proofcarrier is reversed, the stationary transmission ratio always increasesto a negative value with a negative gear set.

In the rotational speed diagram, the rotational speed relationships ofthe individual shafts are plotted in a vertical direction. Thehorizontal gaps between the shafts arise from the transmission ratiorelationships between the shafts, such that rotational speedrelationships and torque relationships of the shafts pertaining to agiven operating point can be connected by a straight line. Thetransmission ratio relationships between the shafts arise from thestationary transmission ratios of the planetary gear sets involved. Therotational speed diagram can be presented, for example, in the form of aKutzbach diagram.

Four shafts designated in the order of rotational speeds as the first,second, third and fourth shafts are characterized in that the rotationalspeeds of such shafts in the specified sequence increase, decrease orare equal in a linear manner. In other words, the rotational speed ofthe first shaft is less than or equal to the rotational speed of thesecond shaft. In turn, the rotational speed of the second shaft is lessthan or equal to the rotational speed of the third shaft. The rotationalspeed of the third shaft is less than or equal to the rotational speedof the fourth shaft. This sequence is also reversible, such that thefirst shaft features the highest rotational speed, while the fourthshaft assumes a rotational speed that is less than or equal to therotational speed of the first shaft. Thereby, there is always a linearrelationship between the rotational speeds of all four shafts.

Thereby, the rotational speed of one or more shafts also assume negativevalues, or even the value of zero. Therefore, the order of rotationalspeeds is always to refer to the signed value of the rotational speeds,and not to their amount or magnitude.

The rotational speeds of the four shafts are equal if, of the elementsring gear, carrier and sun of one of the planetary gear sets, two ofsuch elements are connected to each other.

An electric motor consists at least of one torque-proof stator and onerotatably mounted rotor, and, during engine mode, is configured toconvert electrical energy into mechanical energy in the form ofrotational speed and torque, and, during generator mode, to convertmechanical energy into electrical energy in the form of current andvoltage.

Through shift elements, depending on their operating state, a relativemovement between two components is enabled, or a connection for thetransmission of a torque between the two components is established. A“relative movement” is understood as, for example, a rotation of twocomponents, whereas the rotational speed of the first component and therotational speed of the second component differ from each other. Inaddition, the rotation of only one of the two components is conceivable,while the other component is at a standstill or rotates in the oppositedirection. In the subject invention, the shift elements are preferablydesigned as claw-shift elements, which establish the connection by apositive connection.

Two elements are referred to as connected to each other particularly ifthere is a fixed (in particular, torque-proof) connection between theelements. Such connected elements rotate with the same rotational speed.The various components and elements of the specified invention may beconnected to each other through a shaft or through a locked shiftelement or a connection element, or also directly, for example by awelded connection, a crimping connection or another connection.

Furthermore, two elements are described as connectable if there is adetachably torque-proof connection between such elements. If theconnection exists, such elements rotate with the same rotational speed.

A shifting process is effected by locking a shift element of thetransmission that was previously not located in the power flow of thetransmission, and opening a shift element of the transmission previouslylocated in the power flow of the transmission. The shifting process mayalso be undertaken under load, that is without a complete withdrawal ofthe torque at the transmission input shaft and the transmission outputshaft. Such a shifting process is hereinafter referred to as a “loadshift.” With the use of claw-shift elements, a requirement for a loadshift is that the shift element to be released is guided into a statethat is at least nearly load-free prior to its release. The guiding intothe state that is nearly load-free is achieved by the fact that theshift element is made largely free of torque, such that, through theshift element, no torque or only a small torque is transferred. For thispurpose, through the electric motor, a torque is applied at that shaftwith which the shift element to be released establishes a connection.

Through the connection in accordance with aspects of the invention ofthe rotor to the main gear set, it is thereby achieved that thetransmission ratio of the rotor at the shafts of the main gear set isincreased. If the second shaft of the auxiliary gear set is connected tothe first shaft of the main gear set, through the connection inaccordance with aspects of the invention, the first shaft of the maingear set is always located in the rotational speed plan between firstshaft of the auxiliary gear set and the second shaft of the main gearset. If the second shaft of the auxiliary gear set is connected to thethird shaft of the main gear set, through the suitable selection of thestationary transmission ratio of the planetary gear set of the main gearset, it can also be achieved that, in the rotational speed diagram, thefirst shaft of the main gear set is located between the first shaft ofthe auxiliary gear set and the second shaft of the main gear set.Through this enlarged transmission ratio, the torque to be applied bythe rotor during the shifting process is reduced, by which the electricmotor can be constructed smaller and lighter. In such a manner, with aload shift, the scaled-down electric motor may, even with a high torqueat the transmission input shaft, apply the necessary torque, withoutleading to an undesirably high reduction in torque at the transmissionoutput shaft. The enlarged transmission ratio is also useful if thetorque of the electric motor is to be transferred to the transmissionoutput shaft (for example, when using the transmission in a motorvehicle), by which an electric driving mode of the motor vehicle isenabled. Through the transmission ratio enlarged in such a manner, astart-up of the motor vehicle into an incline is possible even with ascaled-down electric motor. The enlarged transmission ratio is alsouseful if, starting from the electric motor, a torque is transferred tothe transmission input shaft, for example when used for starting aninternal combustion engine that is connected to the transmission inputshaft. Moreover, the enlarged transmission ratio leads to the fact thatthe electric motor is smaller, and thus can be more easily built.

Through the allocation in accordance with aspects of the invention ofthe shafts of the main gear set to the second and third shafts of theauxiliary gear set, it is also achieved that the rotor, even with atorque-proof fixing of one of the shafts of the main gear set, is ableto assume a rotational speed. The assumption of a rotational speed is aprerequisite for the receiving and delivering of mechanical power by theelectric motor. It is thereby enabled that the electric motor is capableof receiving or delivering mechanical power in those gears in which, forexample, the first shaft of the main gear set is fixed in a torque-proofmanner or does not have an appreciable rotational speed. This isparticularly advantageous when using the transmission in a motorvehicle, since kinetic energy of the motor vehicle can be recuperated ineach gear of the transmission through the generator mode of the electricmotor. If an internal combustion engine is connected to the transmissioninput shaft, the load point of the internal combustion engine can alsobe displaced in any gear by the generator mode or engine mode of theelectric motor. Thus, the transmission enables an increase in efficiencyof the motor vehicle.

Preferably, a sun gear of the planetary gear set of the auxiliary gearset is a component of the first shaft of the auxiliary gear set. In theevent that the planetary gear set of the auxiliary gear set is formed asa negative gear set, a carrier of the planetary gear set of theauxiliary gear set is a component of the second shaft of the auxiliarygear set, and a ring gear of the planetary gear set of the auxiliarygear set is a component of the third shaft of the auxiliary gear set. Ifthe planetary gear set of the auxiliary gear set is formed as a positivegear set, the allocation of the ring gear and the carrier isinterchanged, such that the ring gear of the planetary gear set of theauxiliary gear set is a component of the second shaft of the auxiliarygear set, and the carrier of the planetary gear set of the auxiliarygear set is a component of the third shaft of the auxiliary gear set. Indoing so, the rotational speed of the second shaft of the auxiliary gearset is always between the rotational speeds of the first and thirdshafts of the auxiliary gear set, if the specified elements of theplanetary gear set of the auxiliary gear set do not circulate with thesame rotational speed.

Through the multiple number of options offered for the connectionbetween the rotor, the auxiliary gear set and the main gear set, aspectsof the invention are particularly easily adjustable for varioustransmission variants and available installation space ratios.

The first shaft of the main gear set can be fixed in a torque-proofmanner through a fifth shift element. The fourth shaft of the main gearset can be fixed in a torque-proof manner through a sixth shift element.Accordingly, through the fifth and sixth shift elements, a fixedconnection to a transmission housing of the transmission, or to adifferent component of the transmission that is fixed in a torque-proofmanner, can be established. Together with the arrangement of the firstto fourth shift elements, this arrangement results in a particularlyadvantageous allocation of the individual gears.

The sequence of the four shafts of the main gear set in the rotationalspeed diagram depends on the manner in which shafts are allocated towhich elements of the first and second planetary gear sets of the maingear set, and which of the four shafts are connected to each other.Examples of this are known in the state of the art, but certainvariations have emerged as particularly advantageous for implementationin a transmission. These are particularly advantageous based on ageometrically favorable arrangement, based on reduced component stressand based on improved accessibility to the shift elements.

In accordance with a particularly preferred variant, the first shaft ofthe main gear set is connected to the sun gears of the first and secondplanetary gear sets of the main gear set. The second shaft of the maingear set is connected to the carrier of the second planetary gear set ofthe main gear set. The third shaft of the main gear set is connected tothe carrier of the first planetary gear set and to the ring gear of thesecond planetary gear set of the main gear set. The fourth shaft of themain gear set is connected to the ring gear of the first planetary gearset of the main gear set. Thereby, the first and second planetary gearsets are formed as negative gear sets.

In order to simplify the connection between the third shaft of the maingear set and the transmission output shaft, the ring gear of the firstplanetary gear of the main gear set is divided into a first segment anda second segment. Both segments preferably feature the same effectivediameter, by which the same kinematic conditions of the planetary gearset act on both segments. Both segments are components of the fourthshaft of the main gear set. The first segment is connected to thatsection of the fourth shaft of the main gear set that can be fixed in atorque-proof manner by the sixth shift element. The second segment isconnected to that section of the fourth shaft of the main gear set thatis connectable through the first shift element to the first power path.

Between the two segments of the ring gear of the first planetary gearset of the main gear set, one section of the third shaft of the maingear set leads radially outwards. Thereby, the connection of the thirdshaft to the transmission output shaft is facilitated, in particular ifthe transmission output shaft is coaxial to the transmission inputshaft. This is particularly advantageous with a use of the transmissionin a motor vehicle as a component of a drive train arranged in a mannerlongitudinal to the direction of travel.

Preferably, all six shift elements are formed as claw-shift elements,which establish the connection through form closure. Claw-shift elementsare characterized by a negligible loss of power in the open state, bywhich the efficiency of the transmission is significantly improved.

Through the selective meshing of the six shift elements in pairs, eightforward gears can be realized. A first forward gear is formed from thelocking of the third shift element and the sixth shift element. A secondforward gear is formed from the locking of the fourth shift element andthe sixth shift element. A third forward gear is formed from the lockingof the third shift element and the fourth shift element. A fourthforward gear is formed from the locking of the fourth shift element andthe first shift element. A fifth forward gear is formed from the lockingof the third shift element and the first shift element. A sixth forwardgear is formed from the locking of the second shift element and thefirst shift element. A seventh forward gear is formed from the lockingof the third shift element and the second shift element. An eighthforward gear is formed from the locking of the fifth shift element andthe second shift element.

If only the sixth shift element is locked, there is no connectionbetween the transmission input shaft and the transmission output shaft.However, by operating the electric motor, power is transferable betweenthe electric motor and the transmission output shaft. In such a manner,an electrical gear is formed, which, with a reverse rotation of therotor of the electric motor, also serves as a reverse gear. Thus, aseparate reverse gear may be omitted.

Preferably, the transmission may be a component of a hybrid drive trainof a motor vehicle. The hybrid drive train features an internalcombustion engine, in addition to the transmission. The internalcombustion engine is connected or connectable, either directly orthrough a clutch, to the transmission input shaft of the transmission.The motor vehicle may be driven by both the internal combustion engineand the electric motor of the transmission. Optionally, the transmissionfeatures an auxiliary electric motor, which is configured to delivertorque through its rotor to the crankshaft of the internal combustionengine and, in such a way, start the internal combustion engine. Thishas the advantage that the internal combustion engine can be started bythe auxiliary electric motor, without having any influence on asimultaneous electric driving mode, by the motor vehicle being drivensolely by the electric motor of the transmission. If the hybrid drivetrain features a clutch between the transmission and the internalcombustion engine and an auxiliary electric motor, the auxiliaryelectric motor is preferably arranged in the power flow between theinternal combustion engine and the clutch. The clutch may feature avariable torque transfer capacity.

The electric motor is thereby connected to a converter, through whichthe electric motor is connected to an energy storage device. For thispurpose, any form of energy storage device (in particular, anelectrochemical, electrostatic, hydraulic or mechanical energy storagedevice) is suitable.

In an additional embodiment, the transmission may also be a component ofa drive train of an electric motor vehicle. An electric motor vehicle isdriven solely by one or more electric motors, and accordingly has nointernal combustion engine. In this case, a traction electric motor isconnected to the transmission input shaft. Through the differenttransmission ratio stages of the transmission, the traction electricmotor may always be operated in an operating range with a high degree ofefficiency, by which the energy efficiency of the entire electric motorvehicle is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in detail on the basis of theattached figures.

FIG. 1 schematically shows a transmission in accordance with a firstexemplary embodiment of the invention.

FIG. 1a schematically shows a transmission in accordance with anotherexample embodiment of the invention.

FIG. 2 shows a rotational speed diagram of the transmission inaccordance with the first exemplary embodiment.

FIG. 3 shows a shifting diagram of the transmission in accordance withthe first and second exemplary embodiments.

FIG. 4 schematically shows a transmission in accordance with a secondexemplary embodiment of the invention.

FIG. 5 schematically shows a transmission in accordance with a thirdexemplary embodiment of the invention.

FIG. 6 shows a hybrid drive train of a motor vehicle.

DETAILED DESCRIPTION

Reference will now be made to embodiments of the invention, one or moreexamples of which are shown in the drawings. Each embodiment is providedby way of explanation of the invention, and not as a limitation of theinvention. For example, features illustrated or described as part of oneembodiment can be combined with another embodiment to yield stillanother embodiment. It is intended that the present invention includethese and other modifications and variations to the embodimentsdescribed herein.

At the outset, it must be stated that, in the various describedembodiments, the same parts are provided with the same reference signsor the same component names, whereby the disclosures containedthroughout the description can be transferred analogously to the sameparts with the same reference signs or the same component names.

FIG. 1 schematically shows a transmission G in accordance with a firstexemplary embodiment of the invention. The transmission G features anupstream gear set VRS, an auxiliary gear set ZRS and a main gear setHRS. The upstream gear set VRS features a planetary gear set P3, and theauxiliary gear set ZRS features a planetary gear set P4. while the maingear set HRS features a first planetary gear set P1 and a secondplanetary gear set P2. All planetary gear set P1, P2, P3, P4 are formedas negative gear sets.

The presentation of the transmission G essentially shows the connectableand connected elements of the transmission G. Conclusions regarding thetransmission ratio relationships cannot be drawn by the distancesselected in the presentation of the transmission G.

A transmission input shaft GW1 is connected to a sun gear So-P3 of thefirst planetary gear set P3 of the upstream gear set VRS, while a ringgear Ho-P3 of the first planetary gear set P3 of the upstream gear setVRS is connected in a torque-proof manner to the transmission housing GGof the transmission G, or to a different component the transmission Gthat is fixed in a torque-proof manner. In such a way, a first and asecond power path L1, L2 are formed, whereas power from the transmissioninput shaft GW1 can be transferred to the main gear set HRS through boththe first power path L1 and through the second power path L2. The secondpower path L2 thereby transmits to the main gear set HRS a rotationalspeed that is changed compared to the rotational speed of thetransmission input shaft GW1, by translating the rotational speed at thetransmission input shaft GW1 by the transmission ratio between the sungear So-P3 and a carrier St-P3 of the first planetary gear set P3 of theupstream gear set VRS. The first power path L1 transmits the rotationalspeed of the transmission input shaft GW1 without a transmission ratioto the main gear set HRS. Thereby, the sun gear So-P3 of the firstplanetary gear set P3 of the upstream gear set VRS is a component of afirst shaft W1VS of the upstream gear set VRS, which is connected to thetransmission input shaft GW1. The carrier St-P3 of the first planetarygear set P3 of the upstream gear set VRS is a component of a secondshaft W2VS of the upstream gear set VRS. That component on which thering gear Ho-P3 of the first planetary gear set P3 of the upstream gearset VRS is supported is referred to as the third shaft W3VS of theupstream gear set VRS.

The sun gear So-P1 of the first planetary gear set P1 and the sun gearSo-P2 of the second planetary gear set P2 of the main gear set HRS areconnected to each other, and are components of a first shaft W1 of themain gear set HRS. A carrier St-P1 of the first planetary gear set P1 ofthe main gear set HRS is connected to a ring gear Ho-F2 of the secondplanetary gear set P2 of the main gear set HRS and in such a way is acomponent of a third shaft W3 of the main gear set HRS. A ring gearHo-P1 of the first planetary gear set P1 of the main gear set HRS isdesigned in two parts, and thus features a first segment Ho-P1-1 and asecond segment Ho-P1-2, Both segments Ho-P1-1, Ho-P1-2 are components ofa fourth shaft W4 of the main gear set HRS. One section of the thirdshaft W3 of the main gear set HRS runs between the two segments Ho-P1-1,Ho-P1-2 of the ring gear Ho-P1 and thus leads to a transmission outputshaft GW2, which, in the exemplary embodiment shown, is coaxial to thetransmission input shaft GW1. A carrier St-P2 of the second planetarygear set P2 of the main gear set HRS is a component of a second shaft W2of the main gear set HRS. Through this arrangement and connection of theindividual components of the first and second planetary gear sets P1, P2of the main gear set HRS, the arrangement of the first, second, thirdand fourth shafts W1, W2, W3, W4 of the main gear set HRS in therotational speed diagram is determined, whereas the sequence of first,second, third, fourth shafts W1, W2, W3, W4 corresponds to theirsequence in the rotational speed diagram.

The first power path L1 is connectable through a first shift element Ato the fourth shaft W4 of the main gear set HRS and through a secondshift element E to the second shaft W2 of the main gear set HRS. Thesecond power path L2 is connectable through a third shift element B tothe first shaft W1 of the main gear set HRS and through a fourth shiftelement D to the second shaft W2 of the main gear set HRS. The firstshaft W1 of the main gear set HRS is connectable through a fifth shiftelement C to the transmission housing GG of the transmission G, or toanother torque-proof component of the transmission G, such that, with alocked fifth shift element C, the first shaft W1 of the main gear setHRS cannot assume any rotational speed. In the same manner, the fourthshaft W4 of the main gear set HRS can be fixed in a torque-proof mannerthrough a sixth shift element F, by connecting the fourth shaft W4through the sixth shift element F to the transmission housing GG.

In each case, two shift elements can be actuated by a double-actingshift device. The second and fourth shift elements E, D can be actuatedthrough a first shift device. The third and the fifth shift elements B,C can be actuated through a second shift device. The first and sixthshift elements A, F can be actuated through a third shift device.Thereby, each of the three shift devices may occupy three states. In afirst shifting state of the shift device, the first shift elementallocated to the shift device is in a locked position, while the secondshift element allocated to the shift device occupies an open position.In a second shifting state of the shift device, the second shift elementallocated to the shift device is in a locked position, while the firstshift element allocated to the shift device occupies an open position.In a third shifting state, the two shift elements allocated to the shiftdevice occupy the open position. Based on the design of the main gearset HRS and the connection of the main gear set HRS to the electricmotor EM, this allocation of a total of six shift elements A, B, C, D,E, F to only three shift devices is enabled. This reduced number ofshift devices helps to reduce the complexity of the transmission G.

The transmission G features an electric motor EM, whereas a stator S isconnected in a torque-proof manner to the transmission housing GG of thetransmission G or to another torque-proof component of the transmissionG, such that the stator S cannot assume any rotational speed. Arotatably mounted rotor R is connected to a sun gear So-P4 of theplanetary gear set P4 of the auxiliary gear set ZRS. The sun gear So-P4of the planetary gear set P4 of the auxiliary gear set ZRS is acomponent of a first shaft W2P4 of the auxiliary gear set ZRS. A carrierSt-P4 of the planetary gear set P4 of the auxiliary gear set ZRS is acomponent of a second shaft W2P4 of the auxiliary gear set ZRS, and isconnected to the first shaft W1 of the main gear set HRS. A ring gearHo-P4 of the planetary gear set P4 of the auxiliary gear set ZRS is acomponent of a third shaft W3P4 of the auxiliary gear set ZRS, and isconnected to the third shaft W3 of the main gear set HRS.

FIG. 2 shows a rotational speed diagram of the transmission G, while ashifting diagram of the transmission G is shown in FIG. 3. In FIG. 2,the rotational speeds of the four shafts W1, W2, W3, W4 of the main gearset HRS and the rotor R are plotted in a vertical direction in relationto the rotational speed of the transmission input shaft GW1. The maximumarising rotational speed of the transmission input shaft GW1 isnormalized to the value of one. The distances between the four shaftsW1, W2, W3, W4 of the main gear set HRS and the rotor R arise from thestationary transmission ratios of the first and second planetary gearsets P1, P2 of the main gear set HRS and the stationary transmissionratio of the planetary gear set P4 of the auxiliary gear set ZRS.Rotational speed relationships pertaining to a given operating point canbe connected by a straight line.

If two shafts are connected to each other, such shafts connected to eachother rotate with the same rotational speed. For reasons of clarity,such connected shafts can be shown separated from each otherhorizontally in the rotational speed diagram, in order to, for example,better clarify the rotational speed transfer from the upstream gear setVRS through the first or second power paths L1, L2 to the main gear setHRS. The horizontal distance between the connected shafts that isthereby selected in the rotational speed diagram is arbitrary. Ofcourse, the transmission ratio between such connected shafts amounts tothe value of one, independent of the horizontal distance selected in therotational speed diagram.

If, of the ring gear, carrier and sun of a planetary gear set, two ofsuch elements are connected to each other, the ring gear, carrier andsun of such planetary gear set rotate with the same rotational speed. Inthis state, the transmission ratio relationship between the specifiedelements assumes the value of one. For reasons of clarity, thehorizontal arrangement of the shafts connected to such elements is notshifted in the rotational speed diagram. Consequently, this conditioncan be seen in the rotational speed diagram by a horizontal straightline, which connects the participating shafts to each other.

FIG. 3 shows a shifting diagram of the transmission G in accordance withthe first exemplary embodiment. Through the shifting diagram in FIG. 3and the rotational speed diagram in FIG. 2, the operation of the secondexemplary embodiment of the transmission G becomes clear. The lockedshift elements A, B, C, D, E, F are indicated by circles in FIG. 3. Byway of example, the respective transmission ratios of the individualgear steps and the gear jumps to the next higher gear to be determinedfrom them may be taken from the shifting diagram, whereas thetransmission G in such a way has a spread of 10.1. The transmissionratios arise from the stationary transmission ratios of the planetarygear sets P1, P2, P3, P4. Upon a sequential shifting operation, doublegearshifts and group gearshifts can be avoided, since two adjacent gearsteps jointly use one shift element. The gears of the transmission G areshown in the various lines of the shifting diagram. One column of theshifting diagram further indicates whether the electric motor EM in therelevant gear is able to deliver mechanical power to the transmissionoutput shaft GW2, or receive mechanical power from it.

A first forward gear 1VM between the transmission input shaft GW1 andthe transmission output shaft GW2 arises from the locking of the thirdshift element B and the sixth shift element F, a second forward gear 2VMarises from the locking of the fourth shift element and the sixth shiftelement F, a third forward gear 3VM arises from the locking of the thirdshift element B and the fourth shift element D, a fourth forward gear4VM arises from the locking of the fourth shift element D and the firstshift element A, a fifth forward gear 5VM arises from the locking of thethird shift element B and the first shift element A, a sixth forwardgear 6VM arises from the locking of the second shift element E and thefirst shift element A, a seventh forward gear 7VM arises from thelocking of the third shift element B and the second shift element E, andan eighth forward gear 8VM arises from the locking of the fifth shiftelement C and the second shift element E.

In an electric gear 1EM, torque is transferred to transmission outputshaft GW2 solely by the electric motor EM, whereas all shift elementsexcept for the sixth shift element F are open, and there is thus notorque-transferring connection between the transmission input shaft GW1and the transmission output shaft GW2. The electrical gear 1EM alsoserves as a reverse gear, in which the electric motor EM is driven insuch a manner that the rotor R assumes a negative rotational speed; thatis, a reverse rotation. Thus, a separate reverse gear is not necessary.

In the first and second start modes 1S, 2S, torque is supplied to thetransmission input shaft GW1, whereas, depending on the position of thesixth shift element F, torque can be supplied to the transmission inputshaft GW1 exclusively by the electric motor EM or by the transmissionoutput shaft GW2. If the sixth shift element F is locked, and theelectric motor EM does not deliver any torque, the transmission inputshaft GW1 may also be supplied with torque exclusively by thetransmission output shaft GW2. This is particularly relevant when usingthe transmission G in a motor vehicle, in order to, in such a way, startan internal combustion engine VKM connected to the transmission inputshaft GW1. If the sixth shift element F is thereby open, thetransmission output shaft GW2 must be fixed in a torque-proof manner bya parking brake.

In the following, a load-shifting process is described by way ofexample. In the second forward gear, each of the second and the fourthshafts W2, W4 of the main gear set HRS forms a differential shaft, whilethe third shaft W3 of the main gear set HRS represents a sum shaft. Upona shifting process from the second forward gear 2VM to the third forwardgear 3VM, the fourth shift element D is locked. The sixth shift elementF is open; the third shift element B is subsequently locked. If thesixth shift element F is formed as claw-shift element, the sixth shiftelement F must be made largely free of torque prior to opening, suchthat the sixth shift element F only transfers no torque or low torque.This load release of the sixth shift element F is effected by agenerator torque of the electric motor EM. Thereby, at least one portionof the torque previously applied at the third shaft W3 of the main gearset HRS is maintained by which a complete loss of torque does not ariseat the transmission output shaft GW2. If the sixth shift element F isopen, the second shaft W2 of the main gear set HRS becomes the sumshaft, while each of the first shaft W1P4 of the auxiliary gear set ZRSand the third shaft W3 of the main gear set HRS forms a differentialshaft. Through the electric motor EM, a generator torque is now applied,in order to achieve a synchronization of rotational speeds between thesecond shaft W2VS of the upstream gear set VRS and the first shaft W1 ofthe main gear set HRS. This enables a locking of the third shift elementB, whereas at least one portion of the torque previously applied at thethird shaft W3 of the main gear set HRS is maintained. If the thirdshift element B is locked, the first shaft W1 of the main gear set HRSbecomes the differential shaft; the shifting process is thus completed.This ensures that, during the shifting process, one part of the powerflow of the transmission input shaft GW1 at the transmission outputshaft GW2 can be maintained. This mode of operation applies to allembodiments.

FIG. 4 schematically shows a transmission G in accordance with a secondexemplary embodiment of the invention. In contrast to the firstexemplary embodiment, the third shaft W3P4 of the auxiliary gear set ZRSis now no longer connected to the third shaft W3 of the main gear setHRS. Instead, the third shaft W3P4 of the auxiliary gear set ZRS isconnected to the fourth shaft W4 of the main gear set HRS. Thereby, thethird shaft W3P4 of the auxiliary gear set ZRS is connected to thatsection of the fourth shaft W4 of the main gear set HRS that isconnected to the first segment Ho-P1-1 of the ring gear Ho-P1 of thefirst planetary gear set P1 of the main gear set HRS. In order toachieve a transmission ratio effect between the rotor R and the fourshafts W1, W2, W3, W4 of the main gear set HRS that is the same as inthe first exemplary embodiment of the transmission G, the stationarytransmission ratio of the planetary gear set P4 of the auxiliary gearset ZRS must be correspondingly adjusted.

FIG. 5 schematically shows a transmission G in accordance with a thirdexemplary embodiment of the invention. In contrast to the secondexemplary embodiment, the second shaft W2P4 of the auxiliary gear setZRS is now no longer connected to the first shaft W1 of the main gearset HRS. Instead, the second shaft W2P4 of the auxiliary gear set ZRS isconnected to the third shaft W3 of the main gear set HRS. As in thesecond exemplary embodiment, the third shaft W3P4 of auxiliary gear setZRS is connected to the fourth shaft W4 of the main gear set HRS. In thethird exemplary embodiment, the first shaft W1 of the main gear set HRSis located in the rotational speed plan between the first shaft W1 P4 ofthe auxiliary gear set ZRS and the second shaft W2 of the main gear setHRS only if the stationary transmission ratios of the planetary gear setP4 of the auxiliary gear set ZRS and the two planetary gear sets F1, P2of the main gear set HRS are selected accordingly.

The rotational speed plan in FIG. 2 and the shifting diagram in FIG. 4also apply to the second and third exemplary embodiments.

FIG. 6 schematically shows a hybrid drive train of a motor vehicle. Thetransmission G contained therein corresponds to the first exemplaryembodiment of the transmission G, whereas this is to be regarded merelyas an example. A rotatable rotor R2 of an auxiliary electric motor SG isconnected to the transmission input shaft GW1, while the stator S2 ofthe auxiliary electric motor SG is fixed in a torque-proof manner to thetransmission housing GG of the transmission G or to another torque-proofcomponent of the transmission G. Through a rotational vibration damperRD, an internal combustion engine VKM is connected to the transmissioninput shaft GW1. The transmission output shaft GW2 is connected to anaxle drive AG. Starting from the axle drive AG, the torque that appliesat the transmission output shaft GW2 is distributed to wheels W of themotor vehicle. In engine mode of the electric motor EM, electric poweris supplied to the stator S through a power inverter INV, In generatormode of the electric motor EM, the stator S supplies electric power tothe power inverter INV. Thereby, the power inverter INV converts the DCvoltage of a battery BAT into an AC voltage suitable for electric motorEM, and vice versa. Thereby, the auxiliary electric motor SG maylikewise be supplied with electric power through the power inverter INV.Alternatively, the auxiliary electric motor SG may also be connected toa different power supply, for example, to a low-voltage electricalsystem of the motor vehicle.

Modifications and variations can be made to the embodiments illustratedor described herein without departing from the scope and spirit of theinvention as set forth in the appended claims.

REFERENCE SIGNS

-   G Transmission-   GW1 Transmission input shaft-   GW2 Transmission output shaft-   HRS Main gear set-   ZRS Auxiliary gear set-   VRS Upstream gear set-   EM Electric motor-   R Rotor of the electric motor-   S Stator of the electric motor-   SG Auxiliary electric motor-   R2 Rotor of the auxiliary electric motor-   S2 Stator of the auxiliary electric motor-   RD Rotational vibration damper-   VKM Internal combustion engine-   INV Power inverter-   BAT Battery-   P1 First planetary gear set of the main gear set-   P2 Second planetary gear set of the main gear set-   P3 Planetary gear set of the upstream gear set-   P4 Planetary gear set of the auxiliary gear set-   W1 First shaft of the main gear set-   W2 Second shaft of the main gear set-   W3 Third shaft of the main gear set-   W4 Fourth shaft of the main gear set-   W1VS First shaft of the upstream gear set-   W2VS Second shaft of the upstream gear set-   W3VS Third shaft of the upstream gear set-   W1P4 First shaft of the auxiliary gear set-   W2P4 Second shaft of the auxiliary gear set-   W3P4 Third shaft of the auxiliary gear set-   A First shift element-   E Second shift element-   B Third shift element-   Fourth shift element-   C Fifth shift element-   F Sixth shift element-   So-P1 Sun gear of the first planetary gear set of the main gear set-   St-P1 Carrier of the first planetary gear set of the main gear set-   Ho-P1 Ring gear of the first planetary gear set of the main gear set-   Ho-P1-1 First segment-   Ho-P1-2 Second segment-   So-P2 Sun gear of the second planetary gear set of the main gear set-   St-F2 Carrier of the second planetary gear set of the main gear set-   Ho-P2 Ring gear of the second planetary gear set of the main gear    set-   So-F3 Sun gear of the planetary gear set of the upstream gear set-   St-P3 Carrier of the planetary gear set of the upstream gear set-   Ho-F3 Ring gear of the planetary gear set of the upstream gear set-   So-P4 Sun gear of the planetary gear set of the auxiliary gear set-   St-P4 Carrier of the planetary gear set of the auxiliary gear set-   Ho-P4 Ring gear of the planetary gear set of the auxiliary gear set-   L1 First power path-   L2 Second power path-   1VM-8VM First to eighth forward gears-   1EM Electric gear-   1S First start mode-   2S Second start mode-   AG Axle drive-   W Wheel

The invention claimed is:
 1. A transmission, comprising: a transmissioninput shaft; a transmission output shaft; a main gear set, a first powerpath and a second power path formed between the transmission input shaftand the main gear set, the main gear set comprising a first planetarygear set, a second planetary gear set and four shafts, a third shaft ofthe main gear set connected to the transmission output shaft; a firstshift element, the first power path connectable through the first shiftelement to a fourth shaft of the main gear set; a second shift element,the first power path connectable through the second shift element to asecond shaft of the main gear set; a third shift element, the secondpower path connectable through the third shift element to a first shaftof the main gear set; a fourth shift element, the second power pathconnectable through the fourth shift element to the second shaft of themain gear set; an auxiliary gear set, the auxiliary gear set comprisinga planetary gear set and three shafts; and an electric motor having arotor and a stator, a first shaft of the auxiliary gear set connected tothe rotor, wherein a second shaft of the auxiliary gear set isconstantly connected to the first shaft of the main gear set, andwherein a third shaft of the auxiliary gear set is constantly connectedto the third shaft of the main gear set.
 2. The transmission of claim 1,wherein, when the second shaft of the auxiliary gear set is connected tothe third shaft of the main gear set, a stationary transmission ratio ofthe planetary gear set of the auxiliary gear set selected such that thefirst shaft of the main gear set is located between the first shaft ofthe auxiliary gear set and the second shaft of the main gear set in arotational speed diagram.
 3. The transmission of claim 1, wherein: a sungear of the planetary gear set of the auxiliary gear set is a componentof the first shaft of the auxiliary gear set; when the planetary gearset of the auxiliary gear set is a negative gear set, a carrier of theplanetary gear set of the auxiliary gear set is a component of thesecond shaft of the auxiliary gear set, and a ring gear of the planetarygear set of the auxiliary gear set is a component of the third shaft ofthe auxiliary gear set; and when the planetary gear set of the auxiliarygear set is a positive gear set, the ring gear of the planetary gear setof the auxiliary gear set is a component of the second shaft of theauxiliary gear set, and the carrier of the planetary gear set of theauxiliary gear set is a component of the third shaft of the auxiliarygear set.
 4. The transmission of claim 1, further comprising a fifthshift element and a sixth shift element, the first shaft of the maingear set fixable in a torque-proof manner through the fifth shiftelement, and the fourth shaft of the main gear set fixable in atorque-proof manner through the sixth shift element.
 5. The transmissionof claim 4, wherein the first, second, third, fourth, fifth and sixthshift elements are claw-shift elements.
 6. The transmission of claim 4,wherein, through selective closing of the first, second, third, fourth,fifth and sixth shift elements in pairs, eight forward gears arerealizable, a first forward gear arising from locking of the third shiftelement and the sixth shift element, a second forward gear arising fromlocking of the fourth shift element and the sixth shift element, a thirdforward gear arising from locking of the third shift element and thefourth shift element, a fourth forward gear arising from locking of thefourth shift element and the first shift element, a fifth forward geararising from locking of the third shift element and the first shiftelement, a sixth forward gear arising from locking of the second shiftelement and the first shift element, a seventh forward gear arising fromlocking of the third shift element and the second shift element, and aneighth forward gear arising from locking of the fifth shift element andthe second shift element.
 7. The transmission of claim 1, wherein: thefirst and second planetary gear sets of the main gear set are negativegear sets; the first shaft of the main gear set is connected to a sungear of the first planetary gear set of the main gear set and to a sungear of the second planetary gear set of the main gear set; the secondshaft of the main gear set is connected to a carrier of the secondplanetary gear set of the main gear set; the third shaft of the maingear set is connected to a carrier of the first planetary gear set ofthe main gear set and to a ring gear of the second planetary gear set ofthe main gear set; and the fourth shaft of the main gear set isconnected to a ring gear of the first planetary gear set of the maingear set.
 8. The transmission of claim 7, wherein the ring gear of thefirst planetary gear set of the main gear set comprises a first segmentand a second segment.
 9. The transmission of claim 8, wherein onesection of the third shaft of the main gear set is arranged between thefirst and second segments of the ring gear of the first planetary gearset of the main gear set such that the one section of the third shaft ofthe main gear set between the first and second segments is movableradially outwards.
 10. The transmission of claim 1, wherein: theplanetary gear set of the auxiliary gear set and the first and secondplanetary gear sets of the main gear set are negative gear sets; a sungear of the planetary gear set of the auxiliary gear set is a componentof the first shaft of the auxiliary gear set and is connected to therotor; a carrier of the planetary gear set of the auxiliary gear set isconnected to a sun gear of the first planetary gear set of the main gearset and to a sun gear of the second planetary gear set of the main gearset such that the carrier of the planetary gear set of the auxiliarygear set is a component of the second shaft of the auxiliary gear setand the first shaft of the main gear set; a ring gear of the planetarygear set of the auxiliary gear set is connected to a carrier of thefirst planetary gear set of the main gear set and to a ring gear of thesecond planetary gear set of the main gear set such that the ring gearof the planetary gear set of the auxiliary gear set is a component ofthe third shaft of the auxiliary gear set, the third shaft of the maingear set and the transmission output shaft; a ring gear of the firstplanetary gear set of the main gear set is a component of the fourthshaft of the main gear set; and a carrier of the second planetary gearset of the main gear set is a component of the second shaft of the maingear set.
 11. The transmission of claim 1, wherein: the planetary gearset of the auxiliary gear set and the first and second planetary gearsets of the main gear set are negative gear sets; a sun gear of theplanetary gear set of the auxiliary gear set is a component of the firstshaft of the auxiliary gear set and is connected to the rotor; a carrierof the planetary gear set of the auxiliary gear set is connected to asun gear of the first planetary gear set of the main gear set and to asun gear of the second planetary gear set of the main gear set such thatthe carrier of the planetary gear set of the auxiliary gear set is acomponent of the second shaft of the auxiliary gear set and the firstshaft of the main gear set; a ring gear of the planetary gear set of theauxiliary gear set is connected to a ring gear of the first planetarygear set of the main gear set such that the ring gear of the planetarygear set of the auxiliary gear set is a component of the third shaft ofthe auxiliary gear set and the fourth shaft of the main gear set; acarrier of the second planetary gear set of the main gear set is acomponent of the second shaft of the main gear set; and a carrier of thefirst planetary gear set of the main gear set is connected to a ringgear of the second planetary gear set of the main gear set such that thecarrier of the first planetary gear set of the main gear set is acomponent of the third shaft of the main gear set and the transmissionoutput shaft.
 12. The transmission of claim 1, wherein: the planetarygear set of the auxiliary gear set and the first and second planetarygear sets of the main gear set are negative gear sets; a sun gear of theplanetary gear set of the auxiliary gear set is a component of the firstshaft of the auxiliary gear set and is connected to the rotor; a carrierof the planetary gear set of the auxiliary gear set is connected to acarrier of the first planetary gear set of the main gear set and to aring gear of the second planetary gear set of the main gear set suchthat the carrier of the planetary gear set of the auxiliary gear set isa component of the second shaft of the auxiliary gear set, the thirdshaft of the main gear set and the transmission output shaft; a ringgear of the planetary gear set of the auxiliary gear set is connected toa ring gear of the first planetary gear set of the main gear set suchthat the ring gear of the planetary gear set of the auxiliary gear setis a component of the third shaft of the auxiliary gear set and thefourth shaft of the main gear set; a sun gear of the first planetarygear set of the main gear set is connected to a sun gear of the secondplanetary gear set of the main gear set such that the sun gear of thefirst planetary gear set of the main gear set is a component of thefirst shaft of the main gear set; and a carrier of the second planetarygear set of the main gear set is a component of the second shaft of themain gear set.
 13. The transmission of claim 12, wherein stationarytransmission ratios of the planetary gear set of the auxiliary gear setand of the first and second planetary gear sets of the main gear set areselected such that the first shaft of the main gear set is locatedbetween the first shaft of the auxiliary gear set and the second shaftof the main gear set in a rotational speed diagram.
 14. A hybrid drivetrain for a motor vehicle, comprising at least one internal combustionengine and the transmission of claim
 1. 15. The hybrid drive train ofclaim 14, further comprising at least one auxiliary electric motorconnected to the internal combustion engine directly or through thetransmission, the at least one auxiliary electric motor configured tostart the internal combustion engine, the rotor of the auxiliaryelectric motor connected to the transmission input shaft of thetransmission.
 16. A drive train for an electric vehicle, comprising thetransmission of claim
 1. 17. A transmission, comprising: a transmissioninput shaft; a transmission output shaft; a main gear set, a first powerpath and a second power path formed between the transmission input shaftand the main gear set, the main gear set comprising a first planetarygear set, a second planetary gear set and four shafts, a third shaft ofthe main gear set connected to the transmission output shaft; a firstshift element, the first power path connectable through the first shiftelement to a fourth shaft of the main gear set; a second shift element,the first power path connectable through the second shift element to asecond shaft of the main gear set; a third shift element, the secondpower path connectable through the third shift element to a first shaftof the main gear set; a fourth shift element, the second power pathconnectable through the fourth shift element to the second shaft of themain gear set; an auxiliary gear set, the auxiliary gear set comprisinga planetary gear set and three shafts; and an electric motor having arotor and a stator, a first shaft of the auxiliary gear set connected tothe rotor, wherein a second shaft of the auxiliary gear set isconstantly connected to the first shaft of the main gear set, andwherein a third shaft of the auxiliary gear set is constantly connectedto the fourth shaft of the main gear set.
 18. A transmission,comprising: a transmission input shaft; a transmission output shaft; amain gear set, a first power path and a second power path formed betweenthe transmission input shaft and the main gear set, the main gear setcomprising a first planetary gear set, a second planetary gear set andfour shafts, a third shaft of the main gear set connected to thetransmission output shaft; a first shift element, the first power pathconnectable through the first shift element to a fourth shaft of themain gear set; a second shift element, the first power path connectablethrough the second shift element to a second shaft of the main gear set;a third shift element, the second power path connectable through thethird shift element to a first shaft of the main gear set; a fourthshift element, the second power path connectable through the fourthshift element to the second shaft of the main gear set; an auxiliarygear set, the auxiliary gear set comprising a planetary gear set andthree shafts; and an electric motor having a rotor and a stator, a firstshaft of the auxiliary gear set connected to the rotor, wherein a secondshaft of the auxiliary gear set is constantly connected to the thirdshaft of the main gear set, and wherein the third shaft of the auxiliarygear set is constantly connected to the fourth shaft of the main gearset.
 19. The transmission of claim 17, wherein: the planetary gear setof the auxiliary gear set and the first and second planetary gear setsof the main gear set are negative gear sets; a sun gear of the planetarygear set of the auxiliary gear set is a component of the first shaft ofthe auxiliary gear set and is connected to the rotor; a carrier of theplanetary gear set of the auxiliary gear set is connected to a sun gearof the first planetary gear set of the main gear set and to a sun gearof the second planetary gear set of the main gear set such that thecarrier of the planetary gear set of the auxiliary gear set is acomponent of the second shaft of the auxiliary gear set and the firstshaft of the main gear set; a ring gear of the planetary gear set of theauxiliary gear set is connected to a ring gear of the first planetarygear set of the main gear set such that the ring gear of the planetarygear set of the auxiliary gear set is a component of the third shaft ofthe auxiliary gear set and the fourth shaft of the main gear set; acarrier of the second planetary gear set of the main gear set is acomponent of the second shaft of the main gear set; and a carrier of thefirst planetary gear set of the main gear set is connected to a ringgear of the second planetary gear set of the main gear set such that thecarrier of the first planetary gear set of the main gear set is acomponent of the third shaft of the main gear set and the transmissionoutput shaft.
 20. The transmission of claim 18, wherein, when the secondshaft of the auxiliary gear set is connected to the third shaft of themain gear set, a stationary transmission ratio of the planetary gear setof the auxiliary gear set selected such that the first shaft of the maingear set is located between the first shaft of the auxiliary gear setand the second shaft of the main gear set in a rotational speed diagram.21. The transmission of claim 18, wherein: the planetary gear set of theauxiliary gear set and the first and second planetary gear sets of themain gear set are negative gear sets; a sun gear of the planetary gearset of the auxiliary gear set is a component of the first shaft of theauxiliary gear set and is connected to the rotor; a carrier of theplanetary gear set of the auxiliary gear set is connected to a carrierof the first planetary gear set of the main gear set and to a ring gearof the second planetary gear set of the main gear set such that thecarrier of the planetary gear set of the auxiliary gear set is acomponent of the second shaft of the auxiliary gear set, the third shaftof the main gear set and the transmission output shaft; a ring gear ofthe planetary gear set of the auxiliary gear set is connected to a ringgear of the first planetary gear set of the main gear set such that thering gear of the planetary gear set of the auxiliary gear set is acomponent of the third shaft of the auxiliary gear set and the fourthshaft of the main gear set; a sun gear of the first planetary gear setof the main gear set is connected to a sun gear of the second planetarygear set of the main gear set such that the sun gear of the firstplanetary gear set of the main gear set is a component of the firstshaft of the main gear set; and a carrier of the second planetary gearset of the main gear set is a component of the second shaft of the maingear set.
 22. The transmission of claim 21, wherein stationarytransmission ratios of the planetary gear set of the auxiliary gear setand of the first and second planetary gear sets of the main gear set areselected such that the first shaft of the main gear set is locatedbetween the first shaft of the auxiliary gear set and the second shaftof the main gear set in a rotational speed diagram.